[linux-lvm] Problem with UUID, vgscan, vgcfgrestore

[Heinz J. Mauelshagen]

Thanks Andreas for providing this workaround.

The bug causing wrong UUID lists on the PVs has been fixed in LVM 0.9.1 Beta 4
but VGs created/configured with < Beta 4 this still hit us regularly.

It is likely the major reason for the upshowing
"vgscan doesn't find my VGs" problem.

If you send us compressed copies of your LVM metadata (VGDA) taken by

for each pv
do
   of=`basename $pv`
   dd if=$pv of=$of bs=1k count=1000;
   bzip2 $of
done

this will help us to get a better understanding if the above assumption
holds up. We can even provide a vgscan auto uuid update function to
avoid that trouble once we know for sure.

Thanks,
Heinz    -- The LVM Guy --

On Wed, Apr 25, 2001 at 01:51:03PM +0200, David Vidal Rodriguez wrote:
> Oh yes, this procedure has helped me too! I had the same problem and now I can
> use my VG  with no single byte being lost. But from now on I'll start making
> backups of my data... :) Thanks!
> 
> > > OK, I have figured out why vgcfgrestore doesn't work properly with broken
> > > UUIDs.  It is because vgcfgrestore only restores the backup VGDA data to
> > > each disk separately.  This means it is not possible to have consistent
> > > UUIDs generated for all PVs in a VG when vgcfgrestore is run.
> > >
> > > You can try the following (experimental) procedure to fix the UUIDs:
> > >
> > > Check each PV with "pvdata -PP /dev/hdX" to ensure it has a valid
> > > UUID assigned.  Also get the PV numbers (starting with 1) for each of
> > > the PVs.  Finally, check the pv_uuidlist_on_disk.base for each PV.
> > > It will normally be 6144, but it does not have to be.
> > >
> > > for each PV (in PV# order)
> > >     dd if=/dev/hdX bs=1 skip=44 count=128 >> /tmp/uuids
> > >
> > > This should create a file /tmp/uuids which has all of the PV UUIDs in it.
> > > Make sure there are as many UUIDs in the file ("od -a /tmp/uuids" is good)
> > > as you have PVs (8 in your case).
> > >
> > > Now, we want to write the UUID list back to the PVs so vgscan is happy:
> > >
> > > for each PV (in any order)
> > >     dd if=/tmp/uuids of=/dev/hdX bs=1 seek=<pv_uuidlist_on_disk.base for
> > > hdX>
> >
> > Unfortunately this doesn't work. I get on of=/dev/hda2 an invalid argument.
> > Can you write to a partition with dd ? Or has it to be a disk such as
> > /dev/hda ?
> >
> > >
> > > example:
> > >     dd if=/tmp/uuids of=/dev/hda2 bs=1 seek=6144
> > >
> > > Now vgscan should be able to detect all of the disks and work properly.
> > >
> > > Cheers, Andreas
> >
> > _______________________________________________
> > linux-lvm mailing list
> > linux-lvm at sistina.com
> > http://lists.sistina.com/mailman/listinfo/linux-lvm
> 
> --
>   ------------------------------------------------------------------------
>  David Vidal R. (vidalrod at in.tum.de)
>  http://dvr.ismad.com
>  "Ein Computer ohne Windows ist wie ein Fisch ohne Fahrrad."
> 
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm at sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm


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Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen at Sistina.com                           +49 2626 141200
                                                       FAX 924446
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